Absorbing power from the wind represents just one of many different forms of alternative energy. Interest in alternative energy resources has experienced steady increases over the past several decades. This trend stems from the combination of environmental awareness, advances in material science, and the continued increase in the demand for electricity.
Widespread residential electrical service began reaching maturity in the late 1920's as a large portion of the city-dwelling general public consuming electricity on a daily basis. The need for electric supply was large and grew steadily with the advent of population growth and new electrical appliances. In the early years of high electricity use, the demand was met mostly by fossil fuel burning steam power plants and augmented by a few hydroelectric dam sites. Since this time the majority of all electrical power generation has come from the consumption of non-renewable resources; chiefly oil, natural gas, coal, and uranium.
Wind mill use goes back almost a thousand years, seeing the most extensive use in Europe, though there is evidence that the first windmills may have been invented in Persia.[1] The early windmills were constructed chiefly of wood and fabric. These early wind energy devices used massive gear systems to transmit the mechanical power from the propeller shaft to agricultural grinding wheels or other useful devices. The wallower gear, stone nut, and great spur wheels of old have since been replaced by high efficiency gear boxes with precisely machined components made from high strength steels. These improvements alone make wind power cultivation much more practical. Yet, when a 17th century windmill is compared against its modern counterpart the numerous, fundamental similarities prevail.
The most basic difference between the early windmills and modern ones is the nature of the propeller blades. Windmills of old had broad propeller blades whereas modern propeller blades are narrow and long. The old style wide blades were successful in converting linear wind energy to rotational shaft power but were of course much less efficient in doing so than modern windmill blades. The operation of the original wind mills was valuable because it accomplished a task for which the alternative solution was more costly. The alternatives may have been grinding grain manually or using bound livestock to supply the shaft power of the grinding wheel. This principle of cost effectiveness is the ultimate goal of wind power devices in today's world.
The chief competitor to modern windmill energy is electricity that is cheaply produced in mass quantities by a large number of different mechanisms including hydroelectric dams and burning fossil fuels in steam power plants, which were responsible for 3% and 86% of all energy consumed in 2004 respectively.[4] Meanwhile windmill electricity generation accounted for just 0.12% of all electricity production. Windmills rely on highly engineered propeller blades to maximize the torque produced at the propeller shaft. A windmill from centuries past would simply not produce enough power to justify its installation costs.
The wind power industry is dominated by propeller-type windmills. The high cost of modern wind turbines stems in part from the extremely high-tech nature of the propeller blades. Specifically, the lightweight composite materials that are commonly chosen for the construction of the propeller blades are very expensive to obtain and add difficulty while manufacturing the precise geometry of the blades.
Propellers dominate wind energy production mainly because of the huge body of knowledge that has been built up over the past century on propeller design and manufacturing. In other words, the high advancement of propeller technology has caused wind turbine creators to forego other possibilities and choose the known-good science on which to base their products. There is no doubt that these modern windmills are effective in the role of generating electrical power and that they perform a great service for society in replacing more polluting methods of energy production. However, this explanation does not eliminate the need to question whether the industry has gone in the right direction. Might there be a whole different strategy of wind energy absorption that will outperform the propeller driven devices?
Modern, narrow-blade propellers have long been used in high-velocity applications such as aircraft propulsion, but only recently have such propellers seen high-tech design for insertion into low velocity applications. Even an ideally designed propeller can make use of only a small portion of the air that passes through its spatial envelope. One very popular 1.5 Megawatt modern windmill propeller sweeps through a frontal area of 4,070 meter2, though the useful aerodynamic interface comprises less than 8% of that area. Considering all the drawbacks mentioned hereto, it bears explaining why the industry seems devoted to using propeller airfoils exclusively to absorb energy from the wind.
The principle alternative to propellers for the absorption of wind energy is the use of sails and the like. These broad surfaces need not be arranged like centuries old wind mills. The immediate advantage of this change is that they can be produced much more cheaply and easily than the single piece propeller blades, which require precise, expensive manufacturing. Since the initial setup cost is the premiere expense for the life of the product, any significant reduction in this cost will correspondingly increase the economy of energy production overall.[5] However, the cost per unit of energy will also fluctuate with the design and efficiency of the device as a whole.
The avian anatomy uses large, sweeping airfoils very effectively at low velocity, but to mimic a bird's flapping motion would not be entirely useful for producing energy because it would be difficult to transform the flap cycle into rotational shaft work. However, it may be possible to follow the principles of a bird's flapping motion to usefully and efficiently employ large, thin airfoils to collect the energy of the wind.